1. Field of the Invention
The invention relates to catalysts for direct catalytic conversion of cellulose into ethylene glycol, and more particularly to mesoporous carbon supported tungsten carbide catalysts and preparation and applications thereof.
2. Background
Energy is the base of modern society survival and development. The exploitation and utilization of clean energy affects the sustainable development of national economy, and it's the basic guarantee for the national security strategy.
Biomass represents a promising renewable resource. Its utilization and development plays an important role in keeping energy diversity, reducing dependence on fossil oil, and maintaining energy security. Cellulose is the most abundant second generation of biomass resources. It is readily available and inexpensive, e.g., from agricultural wastes and forestry wastes. Meanwhile, cellulose is non-edible and is not a threat to the food security of human being. Therefore, how to convert cellulose into value-added products is a hot research topic among scholars of many nations.
Conventional methods for cellulose conversion focus on hydrolysis in mineral acids or through enzymatic degradation. These methods are of low efficiency and high pollution, therefore facing serious challenges. In comparison, catalytic conversion of cellulose developed in recent years is a highly efficient, green method. The catalytic conversion of cellulose is to degrade cellulose into polyhydroxy compounds in the presence of a catalyst under certain conditions. Professor Fukuoka in Japan used Pt/Al2O3 as the catalyst and obtained 30% yield of hexitols. Employing a Ru/AC catalyst, Professor H. C. Liu of Peking University further improved the hexitol yield to 40% (CN101058531). Professor Y. Wang of Xiamen University achieved a hexitol yield above 50% by pre-treating cellulose in phosphoric acid, regenerating the precipitants using water, and then using a Ru catalyst supported on multiwall carbon nanotubes (MWCNT) in catalytic hydrogenation conversion of cellulose (CN101121643). However, since noble metals were employed in above cases, these methods are of high cost and low economic efficiency.
Recently, we developed a nickel promoted tungsten carbide catalyst loaded on AC for catalytic conversion of cellulose into ethylene glycol under hydrothermal conditions. The reaction is highly efficient with good selectivity, giving the ethylene glycol yield as high as 61%. However, the nickel addition on the catalyst accelerated the tungsten carbide aggregation. Furthermore, the micro structure of AC decreased the dispersion of tungsten carbide on the catalyst and limited the diffusion of reactants and products.
The mesoporous carbon has a relatively high surface area, a large pore volume, is high in acid and alkali resistance and highly hydrothermal stability. Therefore, it is widely used in fuel cell, sensor, adsorption separation, catalysis, and etc.
It is known that the activity and selectivity of a catalyst relates the dispersion of active component and the diffusion of reactants to active sites. Mesoporous carbon supported catalysts promote the dispersion of active metals, increase accessibility of the pores, contribute to molecular diffusion, and consequently increase the activity and selectivity of catalysts. There is no report regarding the application of mesoporous carbon supported tungsten carbide on catalytic conversion of cellulose to ethylene glycol up to now.